The present invention relates to a clutch control system for finite control of a clutch system. More particularly, the present invention relates to a dual gain variable control system for solenoid control of a clutch actuator.
Solenoid control for actuation of drive clutches is known. In control of these clutches, it is desirable to have finite control over certain operational conditions. For instance, a vehicle, when operating in second gear, is under operating conditions wherein there is a lot of torque in the engine and drive train and not much speed of the vehicle. Under these conditions, it is desirable to have higher clamping forces (or fuller engagement of the clutch) and less solenoid finite control is necessary. Whereas, if the vehicle is in 6th gear, it has a lot of speed, but low torque in the engine and drive train. Under these conditions, lower clamping force is necessary and higher finite solenoid control is desired.
Thus, it is desirable in transmission control applications to provide finite resolution at low control pressure while maintaining the capacity to provide high control pressures under certain conditions. Thus, a variable force solenoid pressurizing a clutch requires care in modulating low pressure engagement, while allowing for higher clamping forces to be ramped up fairly quickly once the required engagement force has been attained. Additionally, even higher control pressure may be desired for achieving higher clamping force such as in reverse gear.
In the past, one solution was to use a dual gain solenoid with individually wound coils, such as that shown in U.S. Pat. No. 5,899,436, issued May 4, 1999 to Holmes. While such a construction allows variable control of a clutch unit, the solenoid and control systems used are expensive to manufacture and use. Therefore, it is desirable to provide a substitute solution for providing control of a solenoid.
The present invention provides a method of controlling a proportional solenoid having a single control. The method comprises providing a control signal having a predetermined number of controlled stepped levels. Thereafter, a full gain range is provided, which is between a minimum gain and a maximum gain, for selectively powering the solenoid at any one of the preset gain levels within the full gain range. In the subject invention, the full gain range is selectively reduced to a partial gain range for selectively powering the solenoid. Thereafter, a full gain range is selected in a first mode, or a partial gain range is selected in a second mode, and a power signal is produced to the coil, based on the control signal. The power signal can be either one of the preset number of gain levels in the full range in the first mode, or one of the preset gains in the partial range. This allows the number of preset gains to be the same in the first mode and in the second mode, so that gain levels in the second mode provide a higher resolution than in the first mode.